Sleep loss is associated with significant health risks and financial cost. Fatigue is a major contributor to accidents in all transportation modalities and in a wide range of industrial and medical settings. Research on how fatigue accumulates during sleep loss indicates that it is caused by a combination of extended periods of wakefulness, inadequate restorative sleep, and the displacement of work to times that are not conducive to alert behavior (e.g. night hours, early mornings). Once prior wake extends beyond about 16 hours and/or sleep obtained in the prior 24-hour period is reduced below 5-6 hours, neurobehavioral impairment occurs: people take longer to respond, make more errors, have reduced situational awareness, communicate less effectively, and have increased difficulty making decisions and prioritizing relevant information. While there has been a significant effort directed toward understanding the manner in which fatigue accumulates, remarkably few studies have examined systematically the recovery of sleep and neurobehavioral function in response to sleep loss. It is generally assumed that the sleep system and neurobehavioral function recover at the same rate. Yet, recent research challenges this assumption. Importantly, these studies also demonstrate that there is virtually no understanding of how sleep architecture (e.g. timing and duration of slow wave and rapid eye movement sleep) is related to recovery of neurobehavioral function. Further, it is clear that there is a significant discrepancy between subjective and objective assessments of recovery from sleep loss. The proposed study will evaluate the neurobehavioral effects of one night of sleep loss, then assess the dynamics of varying duration (3, 6 and 9 hours) of recovery sleep opportunities, in terms of both neurobehavioral performance and sleep quality and composition. A total of 104 subjects will be randomly assigned to a control, or one of three recovery groups (N = 26 per group). Following laboratory adaptation and 2 days of baseline sleep and performance measurements, subjects will be deprived of sleep for one night, followed by 7 recovery days/nights. Analyses will focus on group differences in the recovery functions, on hypothesized differential rates of recovery across tasks, and on relationships between the duration and composition of recovery sleep on one hand and neurobehavioral performance levels on the other. This study will be a critical first step toward systematically determining the rate of recovery of neurobehavioral functions following moderate sleep loss. Equally important, the study will further our understanding of the homeostatic and circadian processes that regulate sleep, fatigue, and neurobehavioral functioning. Sleep loss is a major contributor to accidents in all transportation modalities and in a wide range of industrial and medical settings. Yet, little is known about processes involved in recovery from such sleep loss. This study represents a critical first step toward systematically determining how, and at what rate, waking function returns to normal levels following acute sleep deprivation.